It is often difficult to interpret test scores when the test is given in a student's second language. Student proficiency in the second language may then play a significant role in performance on the test, leading to scores reflecting the ability of interest only to the extent that the student possesses the prerequisite language skills for taking the test. This study demonstrates the role of language proficiency as a moderator variable in assessing academic aptitude. It is shown that the strength of the relationship between scores on the SAT® given in English and on the Prueba de Aptitud Academica given in Spanish increases as proficiency in English as a second language increases among students whose first language is Spanish. Scores on tests of student proficiency in English as a second language, like the Test of English as a Foreign Language™ for an international population or the English as a Second Language Achievement Test for an Hispanic population, indicate not only readiness for academic study in English but also the appropriateness of other tests given in English as a basis for admission and placement decisions.